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United States Patent |
6,063,440
|
Chen
,   et al.
|
May 16, 2000
|
Method for aligning a wafer
Abstract
A method for aligning a wafer on a support member within a vacuum chamber
includes increasing the pressure within the vacuum chamber to at least
about 1 Torr before aligning the wafer. The wafer is introduced into the
vacuum chamber on the support member, the pressure is increased to at
least about one Torr, and the support member is lifted into a shadow ring
that has a frustoconical inner cavity constructed to funnel the wafer to a
centered, aligned position.
Inventors:
|
Chen; Ling (Sunnyvale, CA);
Yudovsky; Joseph (Palo Alto, CA);
Yu; Ying (Cupertino, CA);
Lei; Lawrence C. (Milpitas, CA)
|
Assignee:
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Applied Materials, Inc. (Santa Clara, CA)
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Appl. No.:
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893461 |
Filed:
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July 11, 1997 |
Current U.S. Class: |
427/248.1; 118/715; 438/689; 438/758 |
Intern'l Class: |
C23C 016/00 |
Field of Search: |
118/715,723
427/248.1
438/689,758
|
References Cited
U.S. Patent Documents
5326725 | Jul., 1994 | Sherstinsky et al. | 118/728.
|
5516367 | May., 1996 | Lei et al. | 118/725.
|
Other References
U.S. application No. 08/564,398, Marohl et al., Nov. 29, 1995.
U.S. application No. 08/939,962, Lei et al., Nov. 29, 1997.
|
Primary Examiner: Meeks; Timothy
Assistant Examiner: MacArthur; Sylvia R
Attorney, Agent or Firm: Thomason, Moser & Patterson
Claims
What is claimed is:
1. A method for aligning a wafer within a vacuum chamber, comprising:
introducing the wafer into the vacuum chamber;
then increasing the pressure within the vacuum chamber; and
after increasing the pressure within the vacuum chamber, moving the wafer
into alignment with a support member and/or a shadow ring.
2. The method of claim 1, wherein the pressure in the vacuum chamber when
the wafer is introduced therein is 1 milliTorr or less.
3. The method of claim 1, further comprising increasing the pressure in the
vacuum chamber to about 1 Torr.
4. The method of claim 1, further comprising increasing the pressure in the
vacuum chamber to a pressure that is at least about 1 Torr and less than
an operating pressure.
5. The method of claim 1, further comprising increasing the pressure in the
vacuum chamber to a pressure between about 1 Torr and 100 Torr.
6. The method of claim 1, further comprising increasing the pressure in the
vacuum chamber to a pressure between about 1 Torr and 10 Torr.
7. The method of claim 1, further comprising waiting until the pressure
beneath the wafer is equal to or greater than the pressure in the vacuum
chamber before aligning the wafer.
8. A method for aligning a wafer on a support member within a vacuum
chamber, comprising:
providing a shadow ring having a lower portion that is outwardly tapered
for receipt of the wafer and an upper aperture having a diameter that is
slightly less than the outer diameter of the wafer;
introducing the wafer into the vacuum chamber and onto the support member;
increasing the pressure within the chamber; and
subsequently moving the support member toward the shadow ring so that the
shadow ring aligns the wafer on the support member.
9. The method of claim 8, wherein the pressure in the vacuum chamber when
the wafer is introduced therein is 1 milliTorr or less.
10. The method of claim 8, further comprising increasing the pressure in
the vacuum chamber to a pressure about 1 Torr.
11. The method of claim 8, further comprising increasing the pressure in
the vacuum chamber to a pressure that is at least about 1 Torr and less
than an operating pressure.
12. The method of claim 8, further comprising increasing the pressure in
the vacuum chamber to a pressure between about 1 Torr and 100 Torr.
13. The method of claim 8, further comprising increasing the pressure in
the vacuum chamber to a pressure between about 1 Torr and 10 Torr.
14. The method of claim 8, further comprising waiting until the pressure
beneath the wafer is equal to or greater than the pressure in the vacuum
chamber before aligning the wafer.
15. The method of claim 8, further comprising raising the wafer to a
position below the shadow ring before increasing the pressure within the
chamber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of semiconductor wafer
processing equipment. More particularly, the present invention relates to
a method and apparatus for aligning a wafer on a wafer support member.
2. Background of the Related Art
In the fabrication of integrated circuits, the various processes, such as
physical vapor deposition (PVD), chemical vapor deposition (CVD), and etch
processes, are often carried out in a vacuum environment to, among other
things, reduce the particulate level to which the wafers are exposed.
Wafers are introduced into a vacuum processing system through a loadlock
where robots within the vacuum processing system move the wafers from the
loadlock into a transfer chamber and then sequentially through the system
positioning the wafers in a series of processing chambers.
The processing steps carried out within the vacuum chambers typically
require the deposition, or etching of multiple metal, dielectric and
semiconductor film layers on the surface of a wafer. During these
processing steps, one must properly align and secure the wafer in the
processing chamber in which the desired deposition or etch process is
performed.
Typically, the wafer is supported in the chamber on a support member,
commonly called a susceptor or pedestal. The wafer is placed on or secured
to, the upper surface of the support member prior to the deposition or
etch process. To ensure proper processing of the wafer, the wafer must be
properly aligned relative to the support member. The position of the
support member in the chamber is selected to provide a desired spacing and
relative geometry between the generally planar surface of the wafer and
other portions of the process chamber such as a gas plate in a CVD process
or a target in a PVD process.
Generally, a shadow or clamp ring is used to shield the edge of a wafer
and/or, in the case of a clamp ring, secure the wafer to the support
member. Although the present invention is equally applicable to both
shadow rings and clamp rings, the following description will refer
primarily to shadow rings such as those typically used in CVD processes.
In addition to acting as a shield, shadow rings also function in wafer
capturing or alignment on the support member. Wing members extend
downwardly and outwardly from the shadow ring to form a funnel. As the
support member moves the wafer upward into the processing position, the
support member moves the wafer into the funnel which directs the wafer
into alignment with the shadow ring and the support member. Consequently,
the funnel applies vertical and lateral forces to the wafer when the
slanted wing members achieve lateral alignment of a misaligned wafer with
the shadow ring and support member as the support member moves the wafer
to the top end of the funnel and the shadow ring settles on the support
member.
A primary goal of wafer processing is to obtain as many useful die as
possible from each wafer. Many factors influence the processing of wafers
in the chamber and effect the ultimate yield of die from each wafer
processed therein including the existence of contaminants within the
chamber that can attach to the wafer and contaminate one or more die
therein. The processing chambers have many sources of particle
contaminants which, if received on the wafer, reduce the die yield. One
source of particulate contamination occurs when a misaligned wafer is
introduced into the chamber. As the wing members of the shadow ring align
with the wafer, the wafer slides on the flat surface of the support member
and, due to the frictional forces between the wafer and the support
member, may create particulate contaminants. In some cases, the frictional
forces between the wafer and the support member cause the misaligned wafer
to actually move the shadow ring, thereby preventing proper alignment of
the wafer and reducing repeatability of the zone of exclusion shielded by
the shadow ring and the process.
Prior efforts aimed at reducing the creation of particles have reduced the
alignment movement of the wafer on the support member and simply increased
the amount of overhang by the shadow ring. In this way, the shadow ring is
able to cover the wafer without substantial movement of the wafer. One way
that this is accomplished is by increasing the diameter of the shadow ring
funnel upper end so that this diameter is larger relative to the diameter
of the wafer and the support member. Thus, rather than substantially
moving the wafers to align them, these systems simply accept a greater
misalignment and accept greater coverage of the wafer upper surface area.
However, a second factor influencing the processing of wafers in the
chamber and affecting the ultimate yield of die from each wafer processed
therein is the repeatability of the positioning of the wafer and the area
covered by the shadow ring. The wafer must be properly aligned relative to
the support member and the shadow ring to ensure that the film is properly
deposited on the wafer. Therefore, these prior efforts that avoid
alignment of the wafer and cover more surface area are not acceptable.
It would, therefore, be desirable to provide a relatively simple system and
method for reducing the coefficient of friction between the support member
and the wafer that would allow alignment of the wafer without substantial
particle generation.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to provide a
relatively simple apparatus and method for reducing the frictional forces
between the support member and the wafer. It is another object of the
invention to enhance repeatability and to provide a shadow ring that
covers a minimal area of the upper surface of the wafer. Yet another
object of the invention is to provide a system and method for aligning a
wafer that is relatively inexpensive, efficient, simple to implement, and
reliable. Other objects of the invention will become apparent from time to
time throughout the specification and claims as hereinafter related.
The present invention provides methods and apparatuses for aligning a wafer
on a support member in a vacuum chamber. In one aspect of the invention,
the method comprises the steps of introducing the wafer into the vacuum
chamber, increasing the pressure within the vacuum chamber and moving the
wafer into alignment with a support member and/or shadow ring.
In another aspect, the method comprises providing a shadow ring having a
lower portion that is outwardly tapered for receipt of a wafer and an
upper aperture having a diameter that is slightly less than the outer
diameter of the wafer, introducing the wafer into the vacuum chamber and
onto the support member, increasing the pressure within the chamber, and
subsequently moving the support member towards the shadow ring so that the
shadow ring aligns the wafer on the support member.
In accordance with the methods, the apparatus for aligning a wafer on a
support member in a vacuum chamber is an apparatus comprising a support
member positioned within the vacuum enclosure and having a wafer receiving
surface thereon, a shadow ring located within the vacuum chamber, a gas
supply in fluid communication with the vacuum chamber, and a gas flow
controller that controls the flow of gas to the vacuum chamber and,
thereby, regulates the pressure within the vacuum chamber such that, after
the wafer is positioned on the support member and before the wafer is
raised into the shadow ring, the control member raises the pressure within
the chamber to about 1 Torr. The shadow ring used in this apparatus
comprises an upper shield portion defining a circular aperture
therethrough, the circular aperture having a diameter that is slightly
less than the outer diameter of the wafer, a lower portion extending from
the upper shield portion having an annular cross section defining a
frustoconical inner cavity, the diameter of the inner cavity decreases
from a lower mouth aperture to an upper end, and the diameter of the upper
end of the inner cavity is slightly greater than the outer diameter of the
wafer.
In each of these methods and apparatuses, the pressure is preferably raised
to a pressure greater than about 1 Torr and more preferably to a pressure
between about 1 Torr and 100 Torr and most preferably between about 1 Torr
and 10 Torr. Further, the pressure is raised is to approximately equal to
or less than the process pressure. Also, the pressure between the wafer
and the support member is preferably equal to or greater than the pressure
in the chamber before the wafer is aligned.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages and
objects of the present invention are attained and can be understood in
detail, a more particular description of the invention, briefly summarized
above, may be had by reference to the embodiments thereof which are
illustrated in the appended drawings.
It is to be noted, however, that the appended drawings illustrate only
typical embodiments of this invention and are therefore not to be
considered limiting of its scope, for the invention may admit to other
equally effective embodiments.
FIG. 1 is a partial cross sectional view of the vacuum chamber.
FIG. 2 is a schematic drawing of the vacuum chamber and the pressure
control system.
FIG. 3 is a cross sectional view of a typical support member having a wafer
thereon that is partially covered by a shadow ring.
FIG. 4 is a partial, cross sectional view of a shadow ring, a wafer, and a
support member showing the wafer misaligned on the support member as they
enter the inner cavity of the shadow ring.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1, the present invention relates to a method and apparatus
for aligning a wafer 20 on a support member 60 in a vacuum chamber 30. The
alignment apparatus is depicted generally as 10.
The preferred embodiment described below refers to an alignment apparatus
10 that uses a shadow ring 40 to align the wafer 20 on the support member
60. However, the invention is not limited to this precise form of
apparatus for it may apply to any number of alignment mechanisms. As
previously mentioned, the term "shadow ring," as used herein, refers
generally to both shadow rings and clamp rings.
FIG. 1 shows a typical vacuum chamber 30 defined by an outer body 34. The
vacuum chamber 30 houses a support member 60 that may take the form of a
pedestal or susceptor mounted on a generally vertically oriented shaft 62.
The support member 60 serves to support a wafer 20 on its flat upper
supporting surface 69. The support member 60 also includes a step
formation 68 formed on its outer perimeter to receive and support a shadow
ring 40 and includes four finger apertures 66.
In a typical vacuum chamber 30, the pressure within the vacuum chamber 30
is controlled by a pressure control system such as the one shown
schematically in FIG. 2. In this system, a gas supply 170 is provided in
fluid communication with the vacuum chamber 30. A gas flow controller 180
positioned intermediate the gas supply 170 and the vacuum chamber 30
controls the flow from the gas supply 170 to the vacuum chamber 30. Using
a predetermined set of instructions, the gas flow controller 180
selectively provides a flow of gas to the vacuum chamber 30. As the gas
flows into the vacuum chamber 30, the pressure within the vacuum chamber
30 increases. In this way, the gas flow controller 180 controls the
pressure within the vacuum chamber 30. It is possible to provide the gas
to the chamber 30 through the support member 60 to the back side of the
wafer 20. When provided to the back side of the wafer 20, the gas creates
a pressure between the wafer 20 and the support member 60 that is
initially greater than the pressure in the chamber 30. This back side gas
may be provided, for example, by a bypass line 200 that provides
communication from the gas flow controller 180 to the upper surface 64 of
the support member 60 between the support member 60 and the wafer 20.
FIG. 1 also illustrates a wafer lifting finger 90 received in a finger
aperture 66 passing through the body of the support member 60. Typically,
the processing chamber would include four such lifting fingers 90. These
lifting fingers 90 operate to lift the wafer 20 clear of the upper
supporting surface 69 of the support member 60 after processing. This
removal of the wafer 20 is achieved by means of a conventional processing
apparatus robot arm (not shown) which enters the vacuum chamber 30 through
the slit valve opening 36. The same robot arm is also used to insert the
wafers 20 into the vacuum chamber 30. The lifting fingers 90 are movable
vertically under action of a lifting mechanism 92 of which only the upper
portion is shown.
A shadow ring 40 housed within the vacuum chamber 30 operates to provide an
exclusionary zone where no deposition occurs at the edge of the wafer 20.
The shadow ring 40 also operates to force a misaligned wafer 20 into
alignment as the support member 30 moves from a lowered, or idle, position
to a raised, or processing, position. When the support member 30 is in the
lowered position, the shadow ring 40 is supported around its perimeter by
an outer support ring 38 that is, in turn, supported by a conventional
pumping plate 39 attached to the vacuum chamber 30. Together, the two
rings, 40 and 38, divide the vacuum chamber 30 into upper and lower
sections, 30a and 30b respectively.
During processing, the support member 60 moves upward into a raised
position lifting the shadow ring 40. The shadow ring 40 has a lower
portion 42 that rests on the upper surface 69 of the support member 60 and
supports the upper shield portion 50 of the shadow ring 40 above the upper
surface of the wafer 20. Preferably, the shield portion 50 is held about 5
to 10 mils above the wafer 20. The upper shield portion 50 of the shadow
ring 40 defines a circular upper aperture 46 therethrough. The diameter of
the upper aperture 46 may be slightly less than the outer diameter of the
wafer 20 to form the exclusionary zone on the wafer 20. However, new
processes may require no overhang of the shadow ring 40 over the wafer 20.
In one typical processing operation, the step formation 68, shown in FIG.
1, is in the range of 3.8 to 3.9 mm high, the shadow ring 40 is in the
range of 5 to 5.1 mm thick, and the overhanging portion is in the range of
0.8 to 0.9 mm thick. The overhanging portion defines an exclusionary zone
of about 3 to 5 mm about the edge of the wafer 20. However, in the
preferred embodiment, this exclusionary zone is no greater than 1.5 mm
from the edge of the wafer 20. To accommodate the current industry
standards, the exclusionary zone at any one edge is preferably about 1.5
mm or less. This relatively small exclusionary zone is necessary to allow
deposition on the wafer 20 at a position 1.5 mm from the wafer edge.
Industry standards demand a film thickness at 1.5 mm from the wafer edge
that is at least 90 percent of the film thickness at the wafer center. No
deposition is allowed on the beveled edge of the wafer 20. Therefore, for
a typical wafer 20 having a 0.5 mm chamfer about its edge, this allows a
deviation of only about 1 mm from center. As used herein, all dimensions
account for thermal expansion and are representative of measurements at
process temperatures.
Preferably, a purge gas is directed through the support member 60 about the
periphery of the wafer 20. The purge gas flows between the shadow ring 40
and the wafer 20 to help shield the exclusionary zone of the wafer 20.
A lower portion 42 of the shadow ring 40, as shown in FIG. 4, extends
downwardly from the upper shield portion 50. The lower portion 42 has an
annular cross section throughout its length and defines a frustoconical
inner cavity 44 therein that is concentric with the upper aperture 52.
Because wafers 20 are circular in shape, the support member 60 is circular
as is the inner cavity cross section. The diameter of the inner cavity 44
decreases from the lower mouth portion 46 to the upper end 48 of the inner
cavity 44 to form a funnel-like structure for aligning the wafer 20 on the
support member 60. Accordingly, the surface of the inner cavity 44 is
relatively smooth to facilitate the sliding receipt and abutment of the
wafer 20 in the inner cavity 44. To allow receipt of the wafer within
inner cavity 44 and to properly align the wafer 20 with the shadow ring
40, the diameter of the upper end 46 of the inner cavity 44 is slightly
greater than and, preferably, approximately equal to the outer diameter of
the wafer 20. As previously mentioned, current industry practice demands
that the thickness of the deposited film at a position 1.5 mm from the
edge of the wafer 20 be 90 percent of the thickness at the center of the
wafer 20. Accordingly, the wafer 20 must be aligned so that the shadow
ring overhangs the wafer 20 by no more than 1.5 mm about its full
periphery so that the film will be allowed to deposit on the wafer 20 at
1.5 mm from the edge of the wafer 20. Therefore, the diameter of the upper
end 46 of the inner cavity 44 is preferably at most only slightly more
than 3 mm greater than the upper aperture 52 and only slightly greater
than the outer diameter of the wafer 20 to ensure that the edge of the
wafer 20 is within 1.5 mm of the periphery of the upper aperture 52. In
this way, the shadow ring 40 only overhangs the wafer 20 at most by about
1.5 mm about the full periphery of the wafer 20. Because the wafer 20
rests on the upper surface 64 of the support member 60 and the wafer 20 is
relatively thin, the outer diameter of the support member 60 must be
sufficiently small that it can also be positioned proximal the upper end
52 of the inner cavity 44. However, to provide proper support for the
wafer 20, the support member 60 must cover substantially the full area of
the wafer 20. Therefore, the wafer must occupy most of the upper surface
area of the support member 60.
As shown in FIG. 1, once positioned in the vacuum chamber 30, a wafer 20
rests on the upper supporting surface 69 of the support member 30. This
placement is made with the support member 60 in its lowered position.
Before processing may begin, the wafer 20 must first be raised by the
support member 60 to the raised position. It is during the movement from
the lowered position to the raised position that any misalignment of the
wafer 20 is corrected and the wafer 20 is aligned. As the support member
60 moves upward from the lowered position, a misaligned wafer 20 contacts
the inner cavity 44 ofthe shadow ring 40 at a position intermediate the
upper end 48 and the lower mouth portion 46. FIG. 4 illustrates a
misaligned wafer 20 on the support member 60. The point of contact is
dependent upon the magnitude of the misalignment. Preferably, there is no
misalignment. As the support member 60 continues to move upward, the
angled side of the frustoconically-shaped inner cavity 44 exerts a lateral
force on the edge of the wafer 20 forcing the wafer 20 into alignment.
Consequently, when the support member 60 reaches its raised position so
that the wafer 20 is at the upper end 48 of the inner cavity 44 of the
shadow ring 40, the wafer 20 is aligned due to the relative diameters of
the wafer 20 and the shadow ring components. When in this raised position,
depending upon the type of process involved, the outer portion of the
wafer 20 may either bear against the shadow ring 40 and slightly lift the
shadow ring 40 under action of the support member 60 or may rest on the
shoulder 68 of the support member 60 and, thereby, leave a small gap
between the shadow ring 40 and the wafer 20. For convenience, the
application refers primarily to those processes wherein the wafer 20 does
not contact the shadow ring 40 although the present invention is
applicable to all processes. With the support member 60 in the raised
position, the outer portion of the wafer 20 is covered by the upper shield
portion 50 of the shadow ring 40.
However, as mentioned previously, the sliding movement of the wafer 20 on
the support member 60 during alignment creates particles within the vacuum
chamber 30. These particles are generated as a result of the friction
between the wafer 20 and the support member 60 which is generally
characterized by the coefficient of friction of the interface multiplied
by the weight of the wafer 20. Other forces acting upon the wafer 20 also
affect the magnitude of the frictional forces. For example, vacuum
chucking may affect the friction between the wafer 20 and the support
member 60. Likewise, the downward component of the force exerted by the
frustoconical inner cavity 44 increases the frictional forces between the
abutting surfaces. Nevertheless, the friction force between the surfaces
equals the coefficient of friction between the surfaces multiplied by the
downward, normal forces exerted on the wafer 20 whatever their source.
Generally, the weights of the wafers 20 are relatively constant. Greater
frictional forces on the wafer 20 and the support surface 60 cause greater
particle generation and decrease the energy efficiency of the system. In
addition, high frictional forces may cause misalignment and may cause the
wafer 20 to move the shadow ring 40 out of alignment, rather than the
shadow ring 40 moving the wafer 20 into alignment, if the lateral force
applied on the wafer 20 by the shadow ring is insufficient to overcome the
frictional forces. For the purposes of the present application, the
relevant normal and frictional forces are generally characterized by the
following formulas respectively wherein N represents the normal force
applied to the wafer 20, F is the frictional force applied to the wafer
20, G is the weight of the wafer 20, A is the surface area of the wafer
20, P.sub.1 is the pressure in the chamber 30, P.sub.0 is the pressure
between the wafer 20 and the support member 60, and .mu. is the
coefficient of friction.
N=G-(P.sub.1 -P.sub.0)A
F=.mu.N=.mu.(G-(P.sub.1 -P.sub.0)A)
Thus, the normal force is equal to the weight of the wafer 20 less the
force created by the pressure differential on the top and bottom surfaces
of the wafer 20. The force created by this pressure differential equals
the difference between the pressure between the wafer 20 and the support
member 60 and the pressure in the chamber 30 multiplied by the surface
area of the wafer 20. The frictional forces equal the normal forces
multiplied by the coefficient of friction.
Reducing the frictional forces between the wafer 20 and the support member
60 reduces the number of particles generated when the wafer 20 is moved on
the support member 60. Accordingly, in order to reduce the number of
particles generated, the coefficient of friction or the normal force
between the wafer 20 and the support member 60 must be reduced. The
present invention accomplishes this by increasing the pressure within the
vacuum chamber 30 to at least about one Torr. Empirical studies, which are
more fully discussed below, have shown that increasing the pressure within
the vacuum chamber 30, so that the pressure between the wafer 20 and the
support member 60 is equal to or greater than the pressure in the vacuum
chamber 30, reduces the frictional forces between the wafer 20 and the
support member 60. In order for this decrease in frictional force to
occur, one of two things must happen. One possibility is that the
increased pressure somehow lowers the coefficient of friction (e.g., by
possibly creating a cushion of gas between the wafer 20 and the support
member 60). Another possibility is that the increased pressure somehow
lowers the normal force on the wafer 20. Regardless of the manner in which
increasing the pressure affects the frictional forces, the result is that
the frictional forces are reduced and, thus, the wafer 20 may be moved on
the support member 60 with less resistance and less particle generation.
The resulting decrease in frictional force allows freer movement of the
wafer 20 on the support member 60 and, thereby, reduces the resulting
scratches and generated particles. Gas from the gas supply 170 is
introduced into the vacuum chamber 30 to increase the pressure therein.
The gas may be introduced generally into the chamber 30 or through gas
inlets positioned in the upper surface 69 of the support member 60. It is
in this latter case that the pressure below the wafer 20 is greater than
the pressure above the wafer 20.
Therefore, the method of the present invention involves increasing the
pressure within the vacuum chamber 30 to at least about one Torr before
moving the wafer 20 on the support member 60 for alignment. Typically, the
pressure within the vacuum chamber 30 when the wafer 20 is introduced
therein is about one milliTorr or less. The wafer is, thus, introduced
into the vacuum chamber 30 onto the support member 60 which is in a
lowered position. The support member 60 is then raised to the lower mouth
aperture 46 of the shadow ring 40. However, before raising the support
member 60 to the processing position the pressure within the vacuum
chamber 30 is increased to at least about one Torr. Of course, this step
of increasing the pressure may take place at any time before the support
member 60 is raised into the inner cavity 44 of the shadow ring 40.
Preferably, the pressure is raised to between about 1 Torr and 100 Torr
or, more preferably, between about 1 Torr and 10 Torr and approximately
equal to or less than the operating pressure of the process. The operating
pressure of the process is the pressure at which the process, such as a
chemical vapor deposition process, is carried out in the vacuum chamber
30. Also, before raising the support member 60 to the raised position, the
pressure between the wafer 20 and the support member 60 is provided so
that the pressure between the wafer 20 and the support member 60 is
approximately equal to or greater than the pressure in the vacuum chamber
30. Once the pressure in the vacuum chamber 30 is sufficiently raised and
the pressure beneath the wafer 20 is equalized, the support member 60 is
raised to the raised, or processing, position. As previously discussed,
when the support member 60 moves into the shadow ring 40, any misaligned
wafer 20 will contact the angled sides of the inner cavity 44 which will
force the wafer 20 into alignment. After the support member 60 is in the
raised position and the wafer 20 is aligned, the pressure within the
vacuum chamber 30 may be altered as needed.
As previously described, the pressure within the vacuum chamber 30 is
manipulated by a gas supply 170 and a gas flow controller 180. In
operation, the gas flow controller 180 uses predetermined set of
instructions to adjust the pressure within the vacuum chamber 30 as
needed. A vacuum pump 190, or series of vacuum pumps 190, are used to
evacuate the vacuum chamber 30.
EXAMPLE
This system has been tested to determine its effectiveness as follows. A
misaligned wafer 20 was positioned upon a support member 60 in a vacuum
chamber 30 and was raised from a lowered position to a raised position.
The test was conducted under vacuum conditions (i.e., moving the wafer 20
without first increasing the pressure in the chamber) and under
pressurized conditions (i.e., moving the wafer 20 only after increasing
the pressure in the chamber). When tested under pressurized conditions,
the tests were conducted with both the pressure beneath the wafer 20 equal
to and greater than the pressure in the chamber 30. In both of these
pressurized condition tests, the results were essentially the same. The
wafers 20 were then inspected using a SURISCAN 6200 manufactured by Tencor
Instruments to determine the number of particles generated as a result of
the wafer 20 moving on the support member 60. The results revealed that,
without first increasing the pressure in the chamber, alignment of the
wafer generated approximately 50 to 200 particles when the wafer 20
contacted the shadow ring and approximately 5000 backside particles. In
addition, without first increasing the pressure in the chamber, the shadow
ring 40 often moved with the wafer 20 as the support member 60 lifted the
shadow ring 40 due to the frictional forces holding the wafer 20 to the
support member 60. This resulted in a misaligned wafer 20 and reduced
repeatability of the process. However, using the present invention,
wherein the pressure is raised to at least about one Torr before moving
the wafer 20, the movement of the wafer 20 on the support member 60
generated only approximately Twenty (20) particles when the wafer 20
contacted the shadow ring 40 and less than 2000 backside particles.
Further, the misaligned wafer 20 moved on the support member 60 more
readily and was, therefore, properly centered which increased
repeatability of the edge exclusion and the process.
While the foregoing is directed to the preferred embodiment of the present
invention, other and further embodiments of the invention may be devised
without departing from the basic scope thereof, and the scope thereof is
determined by the claims which follow.
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